Ophiuroglypha cf. irrorata (Lyman, 1878)

Bribiesca-Contreras, Guadalupe, Dahlgren, Thomas G., Amon, Diva J., Cairns, Stephen, Drennan, Regan, Durden, Jennifer M., Eleaume, Marc P., Hosie, Andrew M., Kremenetskaia, Antonina, McQuaid, Kirsty, O'Hara, Timothy D., Rabone, Muriel, Simon-Lledo, Erik, Smith, Craig R., Watling, Les, Wiklund, Helena & Glover, Adrian G., 2022, Benthic megafauna of the western Clarion-Clipperton Zone, Pacific Ocean, ZooKeys 1113, pp. 1-110 : 1

Ophiuroglypha cf. irrorata (Lyman, 1878)

Fig. 53

Material.

Clarion-Clipperton Zone • 1 specimen; APEI 7; 4.9081°N, 141.6813°W; 3239 m deep; 26 May. 2018; Smith & Durden leg.; GenBank: ON400685 (COI); NHMUK 2021.21; Voucher code CCZ_058. • 1 specimen; APEI 7; 4.8897°N, 141.75°W; 3096 m deep; 27 May. 2018; Smith & Durden leg.; GenBank: ON400686 (COI); NHMUK 2022.72; Voucher code: CCZ_059 .

Description.

Two specimens, with greyish disc and pale arms in situ (Fig. 53A, B ). Disc rounded to pentagonal, flattened, with slender, long arms, at least disc diameter (disc diameter = 2.6 cm, arm length = 13.1 cm; Fig. 53C, D ). Dorsal disc surface covered by irregular, larger disc scales surrounded by small, imbricated disc scales that also vary in size and shape. Radial shields are small, subtriangular, almost as wide as long. Arm combs visible under the radial shields; with five short block-like arm-comb spinelets, not continuous on dorsal midline. Ventral surface of the disc is covered by large, imbricated scales, increasing in size towards the margin of the disc (Fig. 53F ). Oral plates with 6-8 oral papillae, proximalmost are pointed, becoming block-like towards the distal side of the oral plate. Oral shield approx. as long as wide, subpentagonal, with somewhat concave proximal margins, a convex distal margin, and with lateral margins slightly constricted in the middle, where the genital slit begins. Adoral shields touching proximally, with a similar width all along, and separating the oral shield from the first lateral arm plates. Genital slits run from the middle of the oral shield to the disc margin, bordered by a continuous row of block-like genital papillae that continues dorsally as an arm-comb.

Dorsal arm plates fan-shaped, contiguous. Lateral arm plates bear three short (less than a third of the length of the arm segment) arm spines from the third arm segment; two are located ventrally, very close together, and one located dorsally, approx. halfway through the lateral arm plate; first arm segment bears two arm spines, the second two or three spines. Ventral arm plate trapezoidal, wider than long, only touching the preceding plate only on first three arm segments, after which they are separated by the lateral arm plates and become fan-shaped to rhomboidal, more than twice as wide as long, with pointed proximal edge and rounded distal margin. Towards the distal end of the arms, the second lowest spine is modified into a hyaline hooklet (Fig. 53E ). Tentacle pores only on most proximal segments (8-11), with six ventral and six lateral tentacle scales on first arm segment and decreasing in number until there is a single, very small, spiniform, tentacle scale remaining for most of the arm length.

Remarks.

Both specimens collected are only 0.4% divergent (K2P distance) in COI sequences between them. Closest genetic match is Ophiuroglypha sp. (8% K2P distance) collected in the CCZ ( Christodoulou et al. 2020), and in the phylogenetic tree they were recovered in a well-supported clade along with other species of Ophiuroglypha (Fig. 50 ). Both specimens have an upturned hook in the second lowest arm spine, which is characteristic of species of the genus Ophiuroglypha (previously a subgenus but raised to genus by O’Hara et al. (2018)). Morphologically, the species resembles to Ophiuroglypha irrorata concreta (Koehler, 1901) based on the arm spine arrangement, dorsalmost spine separated from the two ventral spines. However, the DeepCCZ specimens are listed as O. cf. irrorata , as a recent study suggested that the arm spine arrangement might not be species specific, hence questioning the validity of O. irrorata irrorata (Lyman, 1878) and O. irrorata concreta ( Stöhr and O’Hara 2021). Additionally, molecular data has suggested that O. irrorata represents an unresolved complex of species ( Christodoulou et al. 2019).

Ecology.

Both specimens were found on the sedimented seafloor of a seamount in APEI 7, at 3096 (specimen CCZ_059) and 3239 m (specimen CCZ_058) depth.

Comparison with image-based catalogue.

No similar Ophiuroidea morphotypes have been encountered in seabed image surveys conducted in the eastern CCZ nor in abyssal areas of the Kiribati EEZ. Consequently, the in situ images of CCZ_058 and CCZ_059 were catalogued as a new morphotype (i.e., Ophiuroglypha sp. indet., OPH_012).

Phylum Porifera Grant, 1836

A total of eight sponges was collected in the western CCZ. All these belong to the class Hexactinellida and represent seven different species, but none was confidently assigned to any known species. To date, there are 255 records of hexactinellid sponges occurring at> 3000 m depth in the CCZ, with only eight representing preserved specimens ( OBIS 2022). Several genes were targeted for amplification, but only 16S was successfully amplified for all of them. Other genes amplified were COI (7 specimens), 18S (5), 28S (5), and ALG11 (3). Sequences of these genes were combined with the concatenated alignment from Dohrmann (2018), and the phylogenetic tree was estimated using the same parameters (Fig. 54 ).

Class Hexactinellidae Schmidt, 1870

Subclass Amphidiscophora Schulze, 1886

Order Amphidiscosida Schrammen, 1924

Family Hyalonematidae Gray, 1857

Figures

Figure 50. Phylogenetic tree of Ophiuroidea. Concatenated (28 S, and COI) median consensus BEAST tree with posterior probability (PP) and bootstrap (BS) values indicated. Only values of PP> 0.70 and BS> 50 are shown, with values of PP> 0.95 and BS> 90 indicated with a circle. Nodes not recovered on the RAxML tree are indicated with a hyphen. Sequences generated in this study are highlighted in violet.

Figure 53. Ophiuroglypha cf. irrorata (Lyman, 1878). Specimen CCZ _ 059 A in situ image. Specimen CCZ _ 058 B in situ image C dorsal view of specimen before preservation D ventral view E arm hooklets F detail of ventral disc surface and ventral arm plates. Scale bars: 2 cm (A, B); 1 cm (C, D); 2 mm (F). Image attribution: Durden and Smith (A, B); Wiklund, Durden, Drennan, and McQuaid (C-F).

Figure 54. Phylogenetic tree of Hexactinellida. Concatenated (16 S, 18 S, 28 S, and COI) median consensus BEAST tree with posterior probability (PP) and bootstrap (BS) values indicated. Only values of PP> 0.70 and BS> 50 are shown, with values of PP> 0.95 and BS> 90 indicated with a circle. Nodes not recovered on the RAxML tree are indicated with a hyphen. Sequences generated in this study are highlighted in violet.